An effective animal model exists that allows the production of peritoneal mesothelioma in rodents with asbestos and other inorganic fibers. We intend to use this model to investigate the pathogenesis of the disease and obtain data concerning the mechanisms involved, to help guide diagnosis and management of this increasingly important disease. Peritoneal mesothelium exposed to asbestos by either intraperitoneal or intra-abdominal wall administration will be studied in mice serially sacrificed. Investigations will include gross anatomy, histology, histochemistry, conventional electron microscopy, scanning electron microscopy and analytical electron microscopy. Questions to be investigated incude: 1) Is there any favorite site for the primary focus in the induced mesothelioma? (Parietal or visceral layer? Is there any specific location (such as the mesothelium directly covering lymphatic lacunea) to be identified?). 2) Structural and histochemical characterization of the mesothelioma cells at early stages of development. 3) The evolution of the mesothelium from normal to neoplastic. 4) Are abestos fibrils commonly and preferentially seen around the neoplastic mesothelium of the early stages? 5) Identification of floating mesothelioma cells in peritoneal effusions. 6) Response of mesothelioma upon transplantation into nude mice. 7) The comparative pathology of animal and human mesothelioma.